Is there a pre-existing serial package for the Luminary Cortex devices? Or should I just patch together from others (STM ..)?
Luminary micro provide an excellent driver library for all their peripherals. It is included in binary form in the FreeRTOS download, as are many of the header files from which you can get the API. Look in the DemoCommonDriverLuminary directory. You can also download the source with documentation from the Luminary Micro WEB site.
Even if you don't use the drivers exactly as in the library you can use the source code as a reference. The documentation pages on the FreeRTOS site show how to write an ISR on the M3 parts. It is actually much simpler than ARM7 equivalents. You can also use the ISR code included for the Ethernet and other peripherals as examples.
Thhanks for the help!